This invention relates generally to the field of electrical error signal generators and more particularly to the field of electrical signal generators which are capable of generating binary digital streams having predetermined probabilities of error.
Frequently, during the design and testing phases of digital hardware, designers require equipment which will enable them to test the operation and performance of their prototype designs under various error conditions, in order to compare actual and predicted performance. In addition, error testing is a maintenance tool which is commonly used by maintenance personnel to monitor the performance of digital equipment or systems. This is particularly true in the communications industry, where data transmission equipment must operate reliably in the presence of noise. Noise added to digital signals during transmission or produced in equipment, can result in errors in the received data. Consequently, it is common for data transmission systems to employ complicated coding schemes, and error detection and correction circuitry in order to detect and correct errors in the data. Error testing is essential to insure that these circuits are performing properly.
One commonly used error testing technique involves generating known digital data, such as a predetermined code sequence of 1's and 0's, in which one or more bits of the sequence are altered in accordance with some predetermined scheme. The corrupted sequence is then input to the device under test, and the output of the device is compared with the originally generated data, to determine whether or not the errors were detected. Since the performance of equipment is most commonly measured in terms of its probability of detecting errors, it is convenient to be able to generate test sequences having known probabilities of error.
Although test equipment is generally available for this purpose, most commercially available equipment is either costly, difficult to use in terms of being able to set up specific probabilities of error, or limited in the range of error probabilities which it is capable of generating.
It is desirable to have an apparatus which will overcome the aforesaid disadvantages and it is to this end that the present invention is directed. Accordingly, there is provided by the invention, a new and improved apparatus, useful in performing error testing of digital equipment and systems, which is capable of generating digital test signals having specifiable probabilities of error over a large range of probabilities and which is easily implementable in hardware.